The present invention relates to the field of mass storage devices. More particularly, this invention relates to an apparatus and method for producing a stiffer of the E-block or actuator assembly in a disc drive.
One key component of any computer system is a device to store data. Computer systems have many different places where data can be stored. One common place for storing massive amounts of data in a computer system is on a disc drive. The most basic parts of a disc drive are a disc that is rotated, an actuator that moves a transducer to various locations over the disc, and electrical circuitry that is used to write and read data to and from the disc. The disc drive also includes circuitry for encoding data so that it can be successfully retrieved and written to the disc surface. A microprocessor controls most of the operations of the disc drive as well as passing the data back to the requesting computer and taking data from a requesting computer for storing to the disc.
The transducer is typically placed on a small ceramic block, also referred to as a slider, that is aerodynamically designed so that it flies over the disc. The slider is passed over the disc in a transducing relationship with the disc. Most sliders have an air-bearing surface (xe2x80x9cABSxe2x80x9d) which includes rails and a cavity between the rails. When the disc rotates, air is dragged between the rails and the disc surface causing pressure, which forces the head away from the disc. At the same time, the air rushing past the cavity or depression in the air bearing surface produces a negative pressure area. The negative pressure or suction counteracts the pressure produced at the rails. The slider is also attached to a load spring which produces a force on the slider directed toward the disc surface. The various forces equilibrate so the slider flies over the surface of the disc at a particular desired fly height. The fly height is the distance between the disc surface and the transducing head, which is typically the thickness of the air lubrication film. This film eliminates the friction and resulting wear that would occur if the transducing head and disc were in mechanical contact during disc rotation. In some disc drives, the slider passes through a layer of lubricant rather than flying over the surface of the disc.
Information representative of data is stored on the surface of the storage disc. Disc drive systems read and write information stored on tracks on storage discs. Transducers, in the form of read/write heads attached to the sliders, located on both sides of the storage disc, read and write information on the storage discs when the transducers are accurately positioned over one of the designated tracks on the surface of the storage disc. The transducer is also said to be moved to a target track. As the storage disc spins and the read/write head is accurately positioned above a target track, the read/write head can store data onto a track by writing information representative of data onto the storage disc. Similarly, reading data on a storage disc is accomplished by positioning the read/write head above a target track and reading the stored material on the storage disc. To write on or read from different tracks, the read/write head is moved radially across the tracks to a selected target track.
There are two basic types of actuators: linear and rotary. A linear actuator positions the head assembly linearly along a radius of the disk. A rotary actuator, functions much like the tone-arm on a record player, with the actuator positioning the head assembly along an arc over the disc surface. A rotary actuator consists of several components: an E-block assembly, one or more transducer head assemblies, and circuitry for carrying power and signals to and from the transducer head assemblies. The E-block assembly includes one or more arms attached at one end of the E-block, and a yoke which carries a voice coil attached at the other end of the E-block. The E-block also has a bore opening therein for locating a pivot cartridge to allow rotary movement of the E-block assembly. The focus of this invention is on the component referred to as an E-block assembly. The E-block assembly is also commonly referred to as a comb or comb assembly. Specifically, the invention relates to the construction and method of manufacture of E-block assemblies.
Disc drives and their various components are manufactured and marketed in a world wide market where the cost of a disc drive system and its attendant components is a critical parameter in achieving sales of the product. The cost includes factors such as the raw component material, processing (forming, packaging, handling, etc.), recycling of scrap and process wastes, product development, testing, product life, and system performance. Minimizing the cost of a disc drive and its components, such as E-block assemblies, thus encompasses a wide range of design and manufacturing issues.
The material of the component and the method of producing the component clearly has an effect on the cost of the component. Like all manufacturing decisions, the selection of material and method of manufacture requires a tradeoff of costs and advantages to obtain the desired product performance at the lowest cost possible. The parameters for selecting a material and method of manufacture for an E-block of comb assembly in a disc drive can be grouped into three main areas:
1) material and finished product performance,
2) manufacturability, and
3) life expectancy.
Product performance in the disc drive area has several constant goals. Some of the constant goals that effect disc drives include lower access times, increased data capacity and lower use of power by the disc drive. Access time is the amount of time needed to read data from the disc of the disc drive. In most instances, the three manufacturing parameters listed above are optimized to improve the access performance of the disc drive. In other instances, power consumption may be minimized for a given access performance, or access performance may be maximized for a given power consumption.
For disc drive systems, it is desired to maximize the E-block assembly stiffness and minimize the system inertia, because increased stiffness and reduced inertia result in improved access performance (i.e., faster access time and smaller power requirements). A stiffer system will respond faster, as greater stiffness minimizes xe2x80x9csettlexe2x80x9d time at the end of a track access to a desired target track location. The faster a system xe2x80x9csettlesxe2x80x9d, the faster the head assembly can read or write data on the disk at the target track. A low inertia allows an E-block assembly, to be moved quickly from one location to another with a minimum of power consumption. Moving a rotary actuator requires application of torque to the E-block or comb assembly. Torque can be thought of as application of a force at a distance from the axis of rotation of a body. In the instance of an E-block or comb assembly, the force is applied at a distance from the rotatory axis of a pivot cartridge within the bore of the E-block. Torque can also be expressed in terms of inertia of a body as shown in the below listed formula:
T=(J)xc3x97(xe2x88x9d)
where
T=torque
J=inertia of the E-block or comb assembly
xe2x88x9d=angular acceleration of the E-block or comb assembly
From the above formula, it can be seen that reducing the inertia of the E-block or comb assembly results in a lower torque requirement to achieve the same angular acceleration. Lower torque also means less power consumption.
Several mechanical properties determine the stiffness and inertia of a system. These properties are material density, flexural modulus, and specific flexural modulus. A low material density is desired because a low density allows more material to be used to improve the stiffness of the E-block, while maintaining low mass (and thus low inertia). A low material density can reduce cost by eliminating the need for incorporating weight reducing holes into the product. Including weight reducing holes in an E-block requires additional manufacturing steps (such as machining of the component) which add additional costs. Further, the holes may induce air turbulence which effects the performance of the head assemblies as they xe2x80x9cflyxe2x80x9d over the surface of the disk.
A high flexural modulus (MPa), when combined with a low density (kg/m3), produces a higher specific flexural modulus (m2 /s2). Specific flexural modulus is related to the resonance frequency of a structure of a given size and shape, with a high specific flexural modulus indicating a high resonance frequency of the structure. A higher resonance frequency results in improved access performance of the E-block because the assembly may be accelerated harder without inducing resonance of the assembly. Resonance, or vibration of the assembly, increases xe2x80x9csettlexe2x80x9d time which, as discussed above, increases the time required before the head assemblies can read or write data to the disks.
Thermal stability of the E-block is also important in the performance of the disc drive system. As the temperature of a material changes, the material undergoes thermal distortion. In the case of an E-block, thermal distortion causes the arms of the E-block to move relative to a fixed reference point. This thermally induced movement affects the disc drive performance by altering the position of the head assemblies such that they may no longer be able to accurately read and write data to the disks. Ideally, the E-block would suffer no thermal distortion. The next best situation is to minimize the thermal distortion, and use a material that causes all the arms to return to their original positions when the thermal stress is removed. Thus, when selecting a material and method of manufacture for an E-block, the thermal stability of the material and affect of the method of manufacture on thermal distortion are important considerations.
In addition to selecting a material which optimizes the system performance, it is also desired that the component be easy to produce and have a life expectancy at least as long as the life of the assembled product. These three areas (i.e., performance, manufacturability, and life expectancy) each place specific demands on selection of material and method of manufacture. As noted above, to optimize the E-block assembly performance, the material properties relating to density, flexural modulus, specific flexural modulus, and thermal stability are important. For ease of manufacture, material properties such as ultimate strength, yield strength and tensile modulus are important, as well as the ability to assemble, bond, and machine the material. The life of the component is effected by the material""s corrosion resistance and need for surface treatment, and in the case of an E-block assembly, the material""s electrical conductivity. The importance of each of these factors is explained below.
An E-block assembly undergoes a significant amount of handling in transport during the manufacturing process. The component must be sufficiently strong to withstand the handling (and possible abuse) to which it is subjected. Therefore, the ultimate strength and yield strength of the material are important. Some materials used to form E-blocks may be functionally damaged in the manufacturing process without the damage being visible. For example, die cast magnesium has a very low yield strength (103 MPa), with a much higher ultimate strength (220 MPa). Thus a component made of die cast magnesium may yield (i.e., bend) a slight amount but not break. The result of a stress causing bending but not breakage is an unusable component with a defect which may not be detected until late in the manufacturing process, causing a greater manufacturing expense. To avoid this type of damage, a material with a high yield strength and an ultimate strength of essentially the same magnitude is desired. A high yield strength reduces the chance of accidental damage such as bending, while an ultimate strength close to the yield strength is more likely to produce visual evidence of damage. For example, if the yield strength and ultimate strength are equal (i.e., the material is perfectly brittle) any bending will result in a broken part which is easily detected and discarded early in the manufacturing process.
The tensile modulus of the material is important for attaching the head assemblies to the E-block support arms. Head assemblies are often attached by swaging, and it is desired that the E-block assembly material be compatible with the currently used manufacturing processes. For swaging, the material must deflect enough so that the head assembly can be plastically deflected to secure the head assembly to the support arm.
In addition to the above physical properties, it is desired that the material of the E-Block assembly be compatible with current adhesive bonding technologies. Many E-block assemblies have wires or other components bonded to the sides of each arm. The E-block assembly material must be chemically compatible with the chosen adhesives to prevent outgassing and/or corrosion which may damage the disc drive.
The interior of a disc drive is extremely sensitive to foreign materials, such as dust or other particulates. Thus, great care must be taken to ensure such debris is kept out of the disc drive. Particle generation within the disc drive may result in a catastrophic disc crash where the disc drive ceases to function. For metallic E-block assemblies, corrosion products are a significant source of particulates, and some form of surface treatment is required to prevent corrosion of the material. These surface treatments add cost to the finished product, and a product that does not require any special treatment is desirable.
The interior of a disc drive is an electrostatic generator of tremendous potential. When operating, the disks are rotating at a high speed inside a cavity full of dry (non-conducting) air. The rotation of the disks causes the air to rotate also, resulting in dry air moving across the actuator at high speeds. If the actuator and disc assembly are not adequately grounded, an electrostatic charge will build up, eventually dissipating through a circuit of the disc drive. The electrostatic charge may be of a magnitude large enough to destroy the circuit and also the disc drive. To prevent an electrostatic buildup, the material of E-block must be electrically conductive to properly ground the E-block assembly.
A need exists for a process which can be applied to E-blocks made from a material, such as aluminum, which is currently being used and supplied in the disc drive industry. Using current materials keeps the price of the components low and also assures that there are no new manufacturing wrinkles that need to be worked out in order to receive E-blocks from vendors. There is also a need for a process which allows easy, low cost manufacture of the E-block. There is a further need for an E-block assembly capable of exceeding current performance levels. The need is for a stiffer E-block that has a lower inertia. There is a need for an E-block that will require less torque and power to drive during seek operations. There is also a need for an E-block with improved settle time and access time within a disk drive. There is still a further need for an E-block which dissipates static charge and which will not produce particles within the disc drive.
A disc drive, includes a base, a disc stack rotatably attached to the base, and an actuator assembly movably attached to the base. The actuator assembly includes an E-block. The E-block for a disc drive includes a metal core and a ceramic coating on the metal core of the E-block. The ceramic coating on the metal core of the E-block is less dense than the metal core. The stiffness of the ceramic coating on the metal core of the E-block is greater than the stiffness of the metal core. In one embodiment, the E-block has a metal core of aluminum. The ceramic coating is may be formed using any method, including an electrochemical process or by depositing the ceramic coating onto the E-block.
Also disclosed are methods for fabricating an E-block for a disc drive includes the steps of providing a metal E-block and forming a ceramic coating on the E-block. The ceramic coating can be formed using any number of techniques including electrochemical techniques as well as by depositing a ceramic coating onto an E-block.
Advantageously, the method and apparatus described for forming an E-block or comb assembly can be applied to E-blocks made from a commonly used material, aluminum, which is currently being used and supplied in the disc drive industry. As a result, a ready supply of E-blocks or comb assemblies is available which keeps the price of the components low and also assures that there are no new manufacturing wrinkles for manufacturing the unprocessed E-block part. The process allows easy, low cost manufacture of the E-block assembly capable of exceeding current performance levels. The resulting E-block stiffer and has a lower inertia than an E-block made from pure aluminum. As a result, less torque and power are needed to drive the E-block or comb assembly during seek operations. The resulting E-block also has improved settle time over an aluminum E-block. The E-block also has improved access times than a comparable E-block made substantially entirely aluminum. The E-block dissipates static charge and the ceramic coating over the E-block prevents particle generation within the disc drive.